The duplex arrangement of a radio-access technology defines how uplink (mobile-terminal-to-network) and downlink (network-to-mobile-terminal) transmission can co-exist in a telecommunications system. There are basically two duplex schemes available. These are depicted in FIG. 1.
Frequency Division Duplex (FDD) implies that downlink (DL) and uplink (UL) transmissions take place on different frequencies, so-called frequency separation. In case of FDD, downlink and uplink transmission can thus take place simultaneously on the same radio link, i.e. to/from the same mobile terminal.
Time Division Duplex (TDD) implies that downlink and uplink transmission take place in different time slots, so-called time separation. In case of TDD, downlink and uplink transmission can thus take place on the same frequency (non-FDD), i.e. a single frequency is sufficient to support both downlink and uplink transmission.
In case of TDD, the specific sets of time slots assigned for downlink and uplink transmission respectively is referred to as the DL/UL assignment or the DL/UL pattern. Different DL/UL patterns may be configured, e.g. depending on the need for different capacity for downlink and uplink transmission. FIG. 2 illustrates two different DL/UL patterns with a 1:1 DL/UL assignment ratio (one downlink time slot for each uplink time slot) and a 4:1 DL/UL assignment ratio (four downlink time slots for each uplink time slot) respectively.
Typically the period of the DL/UL pattern can be one frame, where a frame may e.g. be of length 10 ms and consist of 10 subframes, each of length 1 ms. This means that the DL/UL pattern repeats itself every frame. However, the DL/UL assignment could also have a longer period, e.g. a period of two frames (20 ms) or four frames (40 ms), implying that the DL/UL pattern repeats itself every 20 ms and every 40 ms respectively.
A special case of FDD operation, i.e. duplex operation with downlink and uplink transmission on different frequencies, is so-called half-duplex operation. Half-duplex operation implies that, from a UE point-of-view, uplink and downlink transmissions do not take place simultaneously, see FIG. 3. Thus, in some sense, half-duplex operation can be seen as a combination of FDD and TDD for a given link. It should be noted though that, on system level and from a base station point-of-view, uplink and downlink transmission may still be simultaneous in case of half-duplex operation within cell.
One reason for employing half-duplex operation is to reduce mobile terminal complexity as the requirements on the terminal, duplex filter can be relaxed. The terminal is also termed user equipment (UE) or mobile station.
One way to implement half-duplex operation is to, for each mobile terminal, assign a DL/UL pattern, similar to TDD as discussed above. This pattern can then be repeated with a period of N frames, where N is a small integer equal to or larger than one, (for example N=1, N=2, or N=4).
In order to efficiently utilize both the uplink and downlink radio resources in case of half-duplex FDD, different mobile terminals should be assigned different DL/UL patterns. This is a result from the fact that, for each subframe, there should be at least one downlink transmission and one uplink transmission. Thus, at least one mobile terminal should be assigned a DL/UL pattern with the given subframe assigned for downlink transmission and at least one mobile terminal should be assigned a DL/UL pattern with the given subframe assigned for uplink transmission. Thus, the two patterns could not be identical.
In contrast, if, for a given subframe, no mobile terminal is assigned a DL/UL pattern with the subframe assigned for uplink transmission, the uplink radio resource is not fully utilized. The same is true for the downlink.
However, in a radio access system, some specific subframes are often used for downlink transmission of so-called system information. The mobile terminals should be able to read this information in order to understand the status of the system, how to access the system, etc. As an example, in Long Term Evolution (LTE) some system information, more specifically the so-called Master Information Block (MIB), is transmitted on the BCH transport channel during the first subframe of each 10 ms frame. Additional system information may be periodically transmitted on the downlink within other subframes.
In case of a periodic DL/UL pattern, with a period being (a multiple of) a frame, there may then be two alternatives:                No mobile terminal is assigned a DL/UL pattern with uplink transmission in subframes where system information is transmitted. The problem with this alternative is that, in these subframes, there can be no uplink transmission and thus uplink radio-resources are thus wasted.        Some mobile terminals are assigned DL/UL patterns with uplink transmission in the subframes where system information is transmitted. These mobile terminals are then not able to read the system information, which is an unacceptable situation as knowledge of the system information is required for proper operation of a mobile terminal.        
As a result from the above there exists a need for a method and a device for assigning DL/UL patterns to mobile terminals in a communications system that removes or reduces one or some of the problems indicated above.